This invention relates to a film unit, which is used for the photography of the multicolor diffusive transfer process type, and more particularly, to a construction of the border of such an image area of a photosensitive laminate as defined by an aperture in a mask constituting the film unit.
Conventionally, in film units for use in the photography of the multicolor diffusive transfer process type (hereinafter referred to as a film unit), there have already been proposed various types of film units as can be found in Japanese Patent Publication (Tokkoshoh) 48-33697, Japanese Laid Open Patent Application (Tokkaishoh) No. 48-43317, Japanese Laid Open Patent Application (Tokkaishoh) No. 50-153628, Japanese Laid Open Patent Application (Tokkaishoh) No. 52-11027, etc. However, their constructions are basically not very different among them, and a typical type is shown in FIGS. 1 and 2 of the accompanyings. FIG. 1 is a perspective view of the film unit of the typical type, while FIG. 2 is an exploded view showing the disassembled state of the components, in which the pod and trap ends have not been folded over yet. As can be seen from these FIGS. 1 and 2, the film unit comprises a photosensitive sheet 1 including a plurality of layers in sequence, which are necessary for an image forming process, a transparent cover sheet 2, a mask 3 defining an image border with an aperture provided therein, a rupturable container or pod member 4 containing an aqueous processing liquid, a trap member 5 capable of retaining therein the surplus processing liquid after the diffusion transfer process and a pair of spacers 6 for use in regulating the thickness of the processing liquid spread over a layer constituting the photosensitive sheet 1. More specifically, according to such film unit as stated hereinabove, the photosensitive sheet 1 comprising layers each having the same dimensions and composed of processing material for its full dimension has applied thereon the following in sequence; i.e. the mask 3 having a rectangular aperture defining the image area, the respective pod member 4 and trap member 5 on both transverse aperture-bordering planes 3d, 3c of the mask 3, the paired spacers 6, 6 on both sides of lateral aperture-bordering planes 3a, 3b of the mask 3 and the transparent cover sheet 2. Accordingly, mask 3, the paired spacers 6, 6, respective pod member 6 and the trap member 5 are sandwiched between the cover sheet 2 and the photosensitive sheet 1, in which the pod and the trap ends of the mask 3 are both folded over in a manner such that these can make the respective pod and trap with respective subsidiary members 4 and 5. The consequent construction of the film unit causes a discharge of the pod's contents to be effectively spread over the photosensitive sheet 1, when subjected to pressure, with a self-processing photographic function being executed.
However, such conventional film units as described hereinabove have the following disadvantages in manufacturing operation and in quality, since the entire region of the photosensitive sheet 1, which relatively faces the cover sheet 2, is composed of several image processing layers.
(1) As can be seen from FIG. 2, such a portion of the photosensitive sheet 1 as covered by the mask 3 (especially, respective portions each superposed thereon either by the bordering plane 3d for construction of the pod or by the bordering plane 3c for construction of the trap) does not serve for the image formation of the self-processing functioning nature. Accordingly, this portion (approximately 37% of the entire area of the photosensitive sheet 1, according to the calculation of the present inventors) is substantially of no use. Although, the detail is specifically described hereinafter, the photosensitive materials required for image formation processing are respectively composed of various kinds of coloring agents, photographic emulsions, etc. Since such materials are commonly composed of such expensive elements as silver or the like, it is to be noted here that the materials required for the above porpose are commonly rather expensive.
(2) When the mask 3 is applied upon the photosensitive sheet 1, a heat-sensitive bonding agent is conventionally used. Such being the case, the mask 3 is superposed on the photosensitive sheet 1 and, is thermally stuck thereon by a heater with a lattice-shaped heating face thereon. As a result, as can be seen in FIG. 3, lattice-shaped heat seal marks 7, which correspond to the structural feature of the heating face of the heater are caused on the plane 3d ready for construction of the pod (when seen from the side of the photosensitive sheet 1).
(3) In the thermal bonding operation between the photosensitive sheet 1 and the mask 3, it is substantially difficult to completely seal the entire faces to be bonded. This means some unsealed portions remain therebetween. Subject to such undesirable sealing condition, the processing liquid may permeate through the unsealed portions, with a result that stripes 8 caused by uneven concentration are effected along the image border definition on the photosensitive sheet 1 as shown in FIG. 3.
(4) Since the mask 3 is superposed on the photosensitive sheet 1, there can be effected stepwise portions on the photosensitive sheet 1 along the aperture of the mask 3 ( i.e. the irregularities occurring along the aperture borders). Hence, when a discharge of the pod's contents (the pod per se is not shown here) is forcibly effected in the direction of the arrows as shown in FIG. 4, air, which has been retained inside the portion between the mask 3 and the sheet 1, is not effectively discharged and thus, involved in the discharge flow, with a result of generation of air bubbles 9 in the stepwise portion. Since the portions of the photosensitive sheet 1 bubbles having thereon are left unprocessed, black dots or black dashes 10 as shown in FIG. 3 are effected along the image border definition on the photosensitive sheet 1.
Recently, in order to especially eliminate the risk of any irregularities occurring along the aperture border, Research Disclosure 78. RD. 17321 discloses several methods for improving the image border definition. According to one embodiment, two opaque and fluid-impervious stripes (carbon-impregnated acrylic material, for example) are applied on the emulsion side of image-receiving member. More specifically, as shown in FIG. 5 of the present drawings, respective stripes 11 are applied on the, portions each superposed thereon, either by the bordering plane 3d for construction of the pod or by the bordering plane 3c for construction of the trap as described earlier. However, to provide such layers 11 as described above, materials and additional manufacturing steps are correspondingly required, thus resulting in higher manufacturing cost of the film unit.
As is clear from the description in the foregoing, the conventional film unit has such disadvantages not only as the manufacturing cost is high due to its non-effective use of the expensive photosensitive material, but also as the consequent photographic products are deteriorated in image quality on the periphery of the image area defined by the aperture in the mask, and such disadvantages have to be eliminated.